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Discussion Starter #1
2005 F250 6.0 w/ 120k miles
Interstate Megatron Batteries, about 18 months old

I've noticed over the past few months that it hasn't seemed to start as quickly as it used to. It wasn't real bad, just something I kinda picked up on. The voltage would be around 11.9v when it first started (which I have heard is normal because the glow plugs draw so much for the first minute or so), and then it would go to 12.8v-ish, and then once I started driving it would go to 13.6-14v. I was starting to think that the slightly slower start was in my head, and it always started, ... until yesterday.

It barely started last night. When it did, my voltage was very low. I have an aftermarket volt meter, and it would just flash "low voltage". I've seen this meter register as low as 10.5, so the voltage had to be even lower than that. Once it started, I kicked on the high idle function (keeps it around 1200 rpm), and the voltage climbed back to normal range. I noticed as I was driving, it would drop to 12.7v-ish at idle, but immediately climb back to 13.7k-ish as soon as the RPMS came back up. After driving for a while, the voltage would stay above 13v even at idle, which I figured is a good sign. But no - once it sits for a while, it starts all over.

I cannot identify anything that would be drawing any significant amount of power when the truck is off. I have a lot of accessories, but they are wired to acc (besides my alarm, which has been on the truck for 2 years).

I'm no expert on this stuff, but since the voltage climbs when I drive, I am tempted to think it's not the alternator. I plan to have the batteries tested today and maybe replaced, since they are under warranty.

But does this sound like it might be the alternator? Or something else? Just the batteries?

Sucks, because I am supposed to leave for a week-long camping trip to Colorado tomorrow morning. I absolutely cannot have this thing give me problems ion the mountain, as I'll be a long way from civilization.

Anyone have insight as to what this is? Thanks.
 

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Have your batteries load tested. Sounds like they are not holding a charge. Have them both tested, replace both if one is bad.

We used interstate in our rental equipment, we quite often had bad luck with them.
 

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The load test will tell the story. A bad cell can show the right voltage but not be able to provide the necessary amps to roll the engine over. That same bad cell will graduly draw the voltage down. Once started the alt puts a surface charge but can't maintain amps.

Sounds like your right on the borderline.
 

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Discussion Starter #4
Thanks guys. I really hope it's just the batteries. I thought these Interstates were supposed to be the bees knees. I'll be getting the same ones, since they are under the free replacement warranty. Shoudl I go to Diehards next time? Is it just hit or miss with batteries?
 

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Honestly, I've always run duralasts from auto zone. Great batteries and an excellent, no hassle warranty. My local AZ will replace both even if one is bad, something most places will not do.
 

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Personally I have seen just about as many top of the line battery failuers as the economy brands. I think proper sizeing, maintenace and inital charge are more important.

Whichever you get take it home and charge it for at least 6 hrs better overnight on a slow charger. The battery in the store is not fully charged, you will get a little more life out of the batteries. On a heavy draw system 2 yrs is generaly the life span of a battery.

Oh you will get some that will last longer and some less but generally.
 

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I was told that one way to tell if your alternator isn't working is to disconnect the batteries while the vehicle is running. If it keeps running, the alternator is good, if it dies, the alternator is bad.

When I had a 'flickering battery' light not too long ago, I used a volt meter at the batteries to see that I was getting just barely 12V after the GPs had shut off and I was running with the RPMs up (foot on the pedal). So, I disconnected the + side of each battery. It kept running with one disconnected, as soon as I disconnected the second batt......shut off. Took the Alt to the parts place, they tested it - Bad. Installed the new one, good to go!! :thumb:

To the OP, it's a quick test.
 

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Easiest thing to do is to hook a multimeter to the back post of the alternator while the truck is running (and everything is connected) to see how many volts it's putting out. If it's "good" (I'd argue a minium is 13.2 - 13.3v), then do somewhere and have your batteries load tested. As mentioned, if one battery is bad you should replace both. Also check the connections and wires for corrosion or other signs that the wire might be compromised, including your ground wires and where they connect to the frame and motor.

My personal preference on batteries is the DieHard Platinum's: 4 year free replacement warranty, a much longer pro-rated warranty, and exceptional ratings and reviews. But if your batteries are still under a free replacement warranty, it doesn't make sense to go spend $500 on two new batteries.

..
 

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Discussion Starter #9
Batteries were shot, got free replacements. Alternator test shows it was going out as well. Just picked up a new 140 amp one from Ford and will be installing tonight.

Vacation saved!

Thanks for all of the replies.
 
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